Coriolis Effect - Dublin Unified School District · The Coriolis effect describes how Earth’s rotation steers winds and surface ocean currents. Unlike land, air and water move freely

Coriolis Effect

Dana Desonie, Ph.D.

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Printed: April 24, 2013

AUTHORDana Desonie, Ph.D.

www.ck12.org Concept 1. Coriolis Effect

CONCEPT 1 Coriolis Effect• Explain the Coriolis effect.

Is this an example of the Coriolis effect?

Does Coriolis determine which direction water in a toilet will swirl? Unfortunately, no. Friction and the power ofthe flush have too big an influence. But in the atmosphere and oceans, Coriolis affects flow direction.

Coriolis Effect

The Coriolis effect is not a force, even though that’s what it is sometimes called. Coriolis does not force anythingto happen! Coriolis is an effect. What does that mean?

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The Coriolis effect describes how Earth’s rotation steers winds and surface ocean currents. Unlike land, air andwater move freely (in the absence of obstacles). The Coriolis effect causes the path of a freely moving object toappear to curve. This is because Earth is rotating beneath the object. So even though the object’s path is straight, itappears to curve. The curve appears to be to the right in the Northern Hemisphere. It appears to be to the left in theSouthern Hemisphere.

Here is an example in the Northern Hemisphere. A plane takes off from City A . The pilot wants to land in City B,which is 500 miles due north. But the plane will not arrive there without corrections. City B was due north of CityA when the plane took off. But during the time it takes for the airplane to fly 500 miles, City B moves east. Thishappens because of Earth’s rotation. So if the airplane flies due north, it will arrive at a different city, City C. City Cis west of City B (in the Northern Hemisphere). To reach City B, the pilot should curve right while flying north. Theopposite happens in the Southern Hemisphere. In the flights between cities pictured below (Figure 1.1), the flightpaths look curved. Since a flight path must curve to the right in the Northern Hemisphere, can you tell which citythe plane took off from in each case?

FIGURE 1.1The Coriolis effect is the reason thatairlines’ flight paths look curved, eventhough they are the shortest possiblepath.

Effect for Air or Water

As wind or an ocean current moves, the Earth spins underneath it. Wind or water that travels toward the poles fromthe Equator curves to the east. Wind or water that travels toward the equator from the poles curves to the west. TheCoriolis effect bends the direction of surface currents to the right in the Northern Hemisphere. The currents curveleft in the Southern Hemisphere (Figure 1.2).

Vocabulary

• Coriolis effect: Apparent deflection of a freely moving object like water or air because of Earth’s rotation.

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www.ck12.org Concept 1. Coriolis Effect

FIGURE 1.2The Coriolis effect causes winds and cur-rents to form circular patterns. The di-rection that they spin depends on thehemisphere that they are in.

Summary

• Earth rotates beneath freely moving objects like water and air. Compared with a spot on the planet, the objectsappear to be moving.

• Freely moving objects appear to move right in the Northern Hemisphere. They appear to move left in theSouthern Hemisphere.

• Coriolis is an effect rather than a force. Coriolis does not force a motion. An object appears to have a changeof motion due to the Coriolis effect.

Practice

Use these resources to answer the questions that follow.

MEDIAClick image to the left for more content.

1. What is the Coriolis effect?2. What is subject to the Coriolis effect?3. What is the direction of deflection in the Northern Hemisphere?4. What is the direction of deflection in the Southern Hemisphere?

Test your skills on the Coriolis effect.

http://www.montereyinstitute.org/noaa/lesson08/l8ex1.htm

5. What happens if pilots do not correct for the Coriolis effect?

Review

1. What is the Coriolis effect?

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2. How does the Coriolis effect explain the curved flight paths in the image above (Figure 1.1)?3. How does Coriolis affect wind and water?

References

1. Image copyright Santiago Cornejo, 2012. . Used under license from Shutterstock.com2. Courtesy of US Navy Oceanographic Office. . Public Domain

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